The French Collection includes many excellent examples of the sources of French law from feudal times. Early French law was derived from the coutumes, as well as from Roman law, and was strongly influenced by canon law, especially in matrimonial and family matters. In addition, royal ordonnances (les ordonnances royaux), and decrees of the Parlement (arrêts du Parlement) which applied generally to the whole of the territory of France, were key sources of law.
By far the most important sources of law were the coutumes, which represent France's earliest efforts to document regional customary laws and practices, and which in turn became an important source of modern French law. At the beginning of the 13th century, these customary laws were still largely oral and lacking in cohesion, but by mid-century, certain of the coutumes made their first written appearance, although official compilations did not appear until the 16th century.
The Library's collection of coutumes is one of the three largest held by academic law libraries in the United States, and includes such important examples as Coustumes de Bretaigne (1540); Nicholas de Bohier's Contenta: Biturigum Consuetudines (1547), a collection of the customary laws of the Touraine and other regions; Charles du Moulin's Le Grand Coustumier Général (1567); La Conférence des Coustumes Tant Générales Que Locales et Particulières du Royaume de France (1596); and Philippe de Beaumanoir's Coustumes de Beauvoisis (1690). Compilations of coutumes in the collection vary widely in physical style from large oversized folios such as Le Droit Commun de la France, et la Coutume de Paris (1770) to tiny duodecimos such as Les Coutumes du Maine (1658), reflecting differences in regional size and influence and the resulting complexity and volume of their documented customary laws.